Those of us who were not in favour of civil partnership, believing that such relationships are harmful to the physical, mental and spiritual wellbeing of those involved, warned that in time marriage would be demanded too. We were accused of scaremongering then, yet exactly such demands are upon us now.

Since all the legal rights of marriage are already available to homosexual couples, it is clear that this proposal is not about rights, but rather is an attempt to redefine marriage for the whole of society at the behest of a small minority of activists.

Redefining marriage will have huge implications for what is taught in our schools, and for wider society. It will redefine society since the institution of marriage is one of the fundamental building blocks of society. The repercussions of enacting same-sex marriage into law will be immense.

But can we simply redefine terms at a whim? Can a word whose meaning has been clearly understood in every society throughout history suddenly be changed to mean something else?

If same-sex marriage is enacted into law what will happen to the teacher who wants to tell pupils that marriage can only mean – and has only ever meant – the union of a man and a woman?

Will that teacher’s right to hold and teach this view be respected or will it be removed? Will both teacher and pupils simply become the next victims of the tyranny of tolerance, heretics, whose dissent from state-imposed orthodoxy must be crushed at all costs?

In Article 16 of the Universal Declaration on Human Rights, marriage is defined as a relationship between men and women. But when our politicians suggest jettisoning the established understanding of marriage and subverting its meaning they aren’t derided.

Instead, their attempt to redefine reality is given a polite hearing, their madness is indulged. Their proposal represents a grotesque subversion of a universally accepted human right.

As an institution, marriage long predates the existence of any state or government. It was not created by governments and should not be changed by them. Instead, recognising the innumerable benefits which marriage brings to society, they should act to protect and uphold marriage, not attack or dismantle it.

This is a point of view that would have been endorsed and accepted only a few years ago, yet today advancing a traditional understanding of marriage risks one being labelled an intolerant bigot.

There is no doubt that, as a society, we have become blasé about the importance of marriage as a stabilising influence and less inclined to prize it as a worthwhile institution.

It has been damaged and undermined over the course of a generation, yet marriage has always existed in order to bring men and women together so that the children born of those unions will have a mother and a father.

This brings us to the one perspective which seems to be completely lost or ignored: the point of view of the child. All children deserve to begin life with a mother and father; the evidence in favour of the stability and well-being which this provides is overwhelming and unequivocal. It cannot be provided by a same-sex couple, however well-intentioned they may be.

Same-sex marriage would eliminate entirely in law the basic idea of a mother and a father for every child. It would create a society which deliberately chooses to deprive a child of either a mother or a father.

Other dangers exist. If marriage can be redefined so that it no longer means a man and a woman but two men or two women, why stop there? Why not allow three men or a woman and two men to constitute a marriage, if they pledge their fidelity to one another? If marriage is simply about adults who love each other, on what basis can three adults who love each other be prevented from marrying?

In November 2003, after a court decision in Massachusetts to legalise gay marriage, school libraries were required to stock same-sex literature; primary schoolchildren were given homosexual fairy stories such as King & King. Some high school students were even given an explicit manual of homosexual advocacy entitled The Little Black Book: Queer in the 21st Century. Education suddenly had to comply with what was now deemed “normal”.

Disingenuously, the Government has suggested that same-sex marriage wouldn’t be compulsory and churches could choose to opt out. This is staggeringly arrogant.

No Government has the moral authority to dismantle the universally understood meaning of marriage.

Imagine for a moment that the Government had decided to legalise slavery but assured us that “no one will be forced to keep a slave”.

Would such worthless assurances calm our fury? Would they justify dismantling a fundamental human right? Or would they simply amount to weasel words masking a great wrong?

The Universal Declaration on Human Rights is crystal clear: marriage is a right which applies to men and women, “the family is the natural and fundamental group unit of society and is entitled to protection by society and the State”.

This universal truth is so self-evident that it shouldn’t need to be repeated. If the Government attempts to demolish a universally recognised human right, they will have forfeited the trust which society has placed in them and their intolerance will shame the United Kingdom in the eyes of the world.

Cardinal O’Brien is President of the Bishops’ Conference of Scotland and Britain’s most senior Catholic.